The proposed research deals with biochemical properties of neurotransmitter receptors in the brain studied by the binding of various radioactive drugs. Dopamine receptors are characterized by binding of 3H-agonists and 3H-antagonists. Regulation of dopamine receptors is apparent with guanine nucleotides. Both norepinephrine alpha and beta-receptors can be labeled with 3H-catecholamines. Agonist interactions with alpha-receptors are also regulated by guanine nucleotides. Histamine receptors in the brain are labeled with 3H-mepyramine.